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Porbeagle Shark Lamna Nasus

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Porbeagle Shark Lamna Nasus Porbeagle Shark Lamna nasus Lateral View (♀) Ventral View (♀) COMMON NAMES APPEARANCE Porbeagle Shark, Atlantic Mackerel Shark, Blue Dog, Bottle-nosed • Heavily built but streamlined mackerel shark. Shark, Beaumaris Shark, Requin-Taupe Commun (Fr), Marrajo • Moderately long conical snout with a relatively large eyes. Sardinero (Es), Tiburón Sardinero (Es), Tintorera (Es). • Large first dorsal fin with a conspicuous white free rear tip. SYNONYMS • Second dorsal fin and anal fin equal-sized and set together. Squalus glaucus (Gunnerus, 1758), Squalus cornubicus (Gmelin, 1789), • Lunate caudal fin with strong keel and small secondary keel. Squalus pennanti (Walbaum, 1792), Lamna pennanti (Desvaux, 1851), Squalus monensis (Shaw, 1804), Squalus cornubiensis (Pennant, 1812), • Dorsally dark blue to grey with no patterning. Squalus selanonus (Walker, 1818), Selanonius walkeri (Fleming, 1828), • Ventrally white. Lamna punctata (Storer, 1839), Oxyrhina daekyi (Gill, 1862), Lamna • Maximum length of 365cm, though rarely to this size. NE MED ATL philippi (Perez Canto, 1886), Lamna whitleyi (Phillipps, 1935). DISTRIBUTION The Porbeagle Shark is a large, streamlined mackerel shark with a In the northern conical snout and powerful body. The first dorsal fin is large and hemisphere, the originates above or slightly behind the pectoral fins. It has a free rear Porbeagle Shark tip which is white. The second dorsal fin is tiny and is set above the occurs only in the anal fin, to which it is comparable in size. The caudal fin is strong and North Atlantic and lunate with a small terminal notch. The caudal keel is strong and, Mediterranean, uniquely for the northeast Atlantic, a smaller secondary caudal keel is whilst in the present. Dorsally, it is dark blue to grey with no patterning. Ventrally it southern is white with darker patterning on the edges of the pectoral fins. The hemisphere it maximum recorded length is 365cm but animals less than 300cm in is found in a length are much more commonly encountered (Compagno, 2001). circumglobal band In European waters it can be confused with the White Shark, (Francis et al, 2008). CR Carcharodon carcharias, the Shortfin Mako Shark. Isurus oxyrinchus, No Records the Longfin Mako Shark, Isurus paucus, and the Blue Shark, Prionace Occasional glauca. However, it is distinguished from all of these species by its Range white free rear tip on the first dorsal fin and the secondary caudal keel. NE ATL: VU ??? Map base conforms with ICES grid squares. Text & Illustrations © Shark Trust 2009 Supported by: Porbeagle Shark SIMILAR SPECIES Carcharodon carcharias, White Shark Isurus oxyrinchus, Shortfin Mako Shark Isurus paucus, Longfin Mako Shark Lamna nasus, Prionace glauca, Blue Shark Porbeagle Shark Carcharodon carcharias, White Shark Isurus oxyrinchus, Shortfin Mako Shark Isurus paucus, Longfin Mako Shark Prionace glauca, Blue Shark (Not to scale) Text & Illustrations © Shark Trust 2009 Porbeagle Shark Lamna nasus TEETH The teeth are moderately large and blade-like with lateral cusps. The first upper lateral teeth have nearly straight cusps (Roman, Unknown). ECOLOGY AND BIOLOGY HABITAT REPRODUCTION The Porbeagle Shark can be found from the surface to 715m in Species in the family lamnidae are viviparous with embryos coastal and pelagic waters (Roman, Unknown). Tagging studies nourished either by a continual supply of unfertilized eggs (oophagy) have revealed a preference for shelf waters, although one tagged or through feeding on less developed siblings (adelphophagy, known individual travelled 1,800km into the mid-Atlantic. There is only only from the Sandtiger Shark, Carcharias taurus) (Martin, 1984). The one record of a tagged shark crossing the Atlantic from Ireland Porbeagle Shark employs oophagy to supply nutrients to embryos to Canada and it appears that the two populations are separate once the original yolk-sac supply has been depleted. Its ovaries are (Francis et al., 2008). While it does not appear to enter freshwater, well adapted to this task and may contain up to 200,000 unfertilised catches from a brackish estuary in Argentina have been reported eggs, measuring 1.5–5mm in diameter (Lombardi, 1998). (Roman, Unknown). It has been reported from the northwest Atlantic that females In the southern hemisphere it may move further north, out of mature at 200–219cm and 50% are mature by 208cm. Males its usual range, during the cooler months but is not found further mature at 155–177cm with 50% mature by 166cm. In the southern north than 35oS during the summer. Around Australia it may move hemisphere off New Zealand, females mature at 170–180cm and into subtropical waters during the winter. It appears to be limited males mature at 140–150cm (Francis et al., 2008). o o to waters between 1–23 C, with abundance declining above 19 C In the North Atlantic mating occurs in autumn and winter and (Francis et al., 2008). the females give birth during spring and summer after an 8–9 In the North Atlantic, temperatures of -1–15oC have been month gestation period. It appears that populations in the southern recorded with a mean of 7–8oC. Its abundance is also governed by hemisphere may breed at different times but data is lacking. The seasonal variations with records of Porbeagles moving north along females give to birth to a litter of 1–5 pups, although 4 is normal with the coast of North America during the spring and early summer 2 pups to each uterus. Each of these pups measures 58–67cm long at with the return migration in late autumn (Francis et al., 2008). birth (Francis et al., 2008). The Porbeagle Shark appears to segregate by sex and size. In Spanish waters, males dominate catches over females in a ratio of 2:1, while 30% more females than males are caught off Scotland. In the Bristol Channel, smaller individuals are found with a dominance of males over females (Francis et al., 2008). This segregation is likely to have evolved as a mechanism of reducing predation of neonates by adults and also to limit breeding to appropriate seasons (Roman, Unknown). DIET The Porbeagle Shark is primarily a piscivore with teleost fish constituting 90% of the diet of some individuals. It has been reported that pelagic fish are preferred during the spring and summer when abundant. During the autumn and winter, groundfish are the dominant prey. (Roman, Unknown). Compagno (2001) lists the most common prey items as mackerels, pilchards and herring, various gadoids including cod, hakes, haddock, cusk, and whiting, and john dories, dogfishes and hound sharks (Squalus and Galeorhinus spp.), and squids (Compagno, 2001). Text & Illustrations © Shark Trust 2009 Supported by: Porbeagle Shark COMMERCIAL IMPORTANCE IUCN RED LIST ASSESSMENT One of the most valuable elasmobranch species to commercial Vulnerable (2005). fisheries, the Porbeagle Shark is taken across its range in targeted Critically Endangered in northeast Atlantic. longline fisheries and its flesh is used for human consumption, its fins for sharkfin soup, its liver oil for vitamins and its carcass can be processed for fishmeal. It is also regularly taken as bycatch, particularly in tuna longline fisheries in the South Pacific but also in trawl, handline and gillnet fisheries. It is an important recreational species on both sides of the North Atlantic (Stevens et al., 2006). THREATS, CONSERVATION, LEGISLATION HANDLING AND THORN ARRANGEMENT The Porbeagle Shark has been fished commercially since the early • Handle with care. 1800’s, principally by Scandinavian fishers, to provide flesh for • Large shark. human consumption, fins for sharkfin soup, liver oil for vitamins • Powerful jaws and sharp teeth. and carcass’ for fishmeal (Gauld, 1989). Global catches peaked in the 1960’s at around 9,000 tons, followed by a rapid decline to 1,300– • Abrasive skin. 2,600 tons in the 1990’s (Francis et al., 2008). Catches in the North Atlantic have varied wildly during the 20th century, particularly in the case of the Norwegian targeted fishery. In 1926, 279 tons were landed. This increased to 3,884 tons in 1933 followed by a sharp decline due to the reduction in fishing effort during the Second World War. In 1947, catches were back up to 2,824 tons but then declined steadily to 207 tons in 1970 and just 25 tons in 1994. The fishery attempted to boost catches by moving across to the west Atlantic stock but had to switch focus to other species such as the Shortfin Mako Shark, Isurus oxyrinchus, and swordfish (Compagno, 2001). Currently in the North Atlantic, the Porbeagle Shark is taken primarily in directed longline fisheries, although there is some bycatch from bottom trawls, handlines and gill nets. The majority of the catch in the southern hemisphere is bycatch from tuna longline fleets in the South Pacific and southern Indian Ocean, although there is a small Norwegian targeted fishery (Francis et al., 2008). The only landings reported to the FAO from the southern hemisphere are from the New Zealand fishery, meaning that the fishing mortality for the southern stock is almost unknown (Compagno, 2001). In the northeast Atlantic, the Porbeagle Shark is covered by EC Regulation No. 1185/2003 which prevents the removal of its fins at sea and the subsequent discard of the body. This applies to all vessels operating in EC waters, as well as to EC vessels operating anywhere (CPOA Sharks, 2009). In addition, a total allowable catch (TAC) applies to this species in European Waters. In 2008 this TAC was 581 tons. Despite scientific advice for a zero TAC for 2009, it was lowered by only 25% to 436 tons with a maximum landing size of 210cm designed to protect breeding individuals (European Commission, 2008). In 2010, the TAC was finally reduced to zero meaning the species cannot be landed by commercial fishers in the EU. Text & Illustrations © Shark Trust 2009 Porbeagle Shark Lamna nasus REFERENCES COMPAGNO, L.
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